Jen was Vince Vincente's late lover.
In the past, Vince mistreated Jen by abandoning her many times. Vince did not truly regret his bad behavior until Jen left him and later committed suicide by swallowing pills.
As a result, Vince began drinking and could not truly enjoy his rock star life, as he longed only to take back what he had failed to keep.
The archangel Lucifer took advantage of this longing by taking Jen's form when he appeared to Vince, and told Vince that he and Jen could be together so long as he "let her in". This led to Vince's possession by Lucifer.